1. Field of the Invention
The present invention relates to a condensation system for use in a power plant including a steam generator and a steam turbine, and more particularly to a condensation system comprising a side stream condenser defining therein first and second hot wells with the first hot well receiving therein condensate produced by condensing steam exhausted from the steam turbine.
2. Description of Prior Art
A conventional condensation system of the kind described above comprises a condensate purification system which includes a condensate feed line through which condensate is fed from the first hot well to the second hot well, a condensate pump in the condensate feed line, a condensate purifying apparatus provided in the condensate feed line at a location downstream of the condensate pump for removing impurities from the condensate and subjecting thereto a PH control, and a return line having one end thereof connected to the first hot well and the other end connected through a first flow control valve to the condensate feed line at a location downstream of the condensate purifying apparatus. A second flow control valve is provided in a branch line which has one end thereof connected to the condensate feed line at a location downstream of the location where the other end of the return line is connected to the condensate feed line and the other end connected to the return line at a location downstream of the first flow control valve.
The conventional condensation system further comprises a supplementary feed system which includes a condensate tank, a supplementary feed line communicating the tank and the first hot well with each other, a supplementary feed valve provided in the supplementary feed line for controlling flow rate of condensate supplied from the tank into the first hot well, a spill-over line having one end thereof connected to the tank and the other end connected to a main condensate feed line of a main feed system, and a spill-over valve provided in the spill-over line for controlling flow rate of condensate introduced from the main condensate feed line into the tank. Condensate is supplied from the second hot well to the steam generator through the main condensate feed line.
Control system for the condensing system includes a first level detector for detecting level of condensate in the first hot well to produce a signal, a second level detector for detecting level of condensate in the second hot well to produce a signal, a first actuator operative in response to the signal from the first detector to actuate the first and second flow control valves so as to regulate the respective opening degrees thereof, and a second actuator operative in response to the signal from the second level detector to actuate the supplementary feed valve and the spill-over valve so as to regulate the respective opening degrees thereof.
With such arrangement of the conventional condensation system, a signal which indicates change in level of condensate in the first hot well is introduced from the first level detector into the first and second flow control valves to adjust the rate of flow rate of condensate returned into the first hot well to flow rate of condenate fed into the second hot well. In addition, a signal which indicates change in level of condensate in the second hot well is introduced from the second level detector into the supplementary feed valve to regulate flow rate of condensate supplied from the tank to the first hot well. Thus, the level of condensate in the first hot well is controlled by the regulation of flow rate of condensate returned into the first hot well through the return line and the regulation of flow rate of condensate supplied to the first hot well through the supplementary feed line.
However, the change in flow rate of condensate returned into the first hot well through the return line causes flow rate of condensate introduced to the second hot well through the condensate feed line to be changed. Accordingly, the control of level of condensate in the first hot well affects the level of condensate in the second hot well. In addition, since the level of condensate in the first hot well is also controlled by the supplementary feed valve which is actuated in response to the signal from the second level detector, responsibility of control of level of condensate in the first hot well is low.
Furthermore, the signal from the second level detector is also introduced into the first and second flow control valves to adjust the rate of flow rate of condensate returned into the first hot well to flow rate of condensate fed into the second hot well. The signal from the second level detector is introduced into the spill-over valve to regulate flow rate of condensate introduced from the main condensate line to the tank through the spill-over line. Thus, the level of condensate in the second hot well is controlled by the regulation of flow rate of condensate supplied into the second hot well through the condensation feed line and the regulation of flow rate of condensation introduced from the main condensate line to the tank through the spill-over line. However, the change in flow rate of condensate supplied to the second hot well through the condensate feed line causes flow rate of condensate returned into the first hot well through the return line to be changed. Accordingly, control of level of condensate in the second hot well affects the level of condensate in the first hot well.
Furthermore, in the conventional condensation system, halt or unactivation of the main condensate pump makes it impossible to control the level of condensate in the second hot well, because the condensate is no longer introduced from the main feed line to the tank through the spill-over line.